As the need for increased data storage changes, the search for higher density, faster access memory technologies also increases. One of these, holographic data storage, provides the promise for increased access to higher density data. The techniques for realizing such storage typically utilize some type of storage media, such as photorefractive crystals or photopolymer layers, to store 3-D stacks of data in the form of pages of data. Typically, coherent light beams from lasers are utilized to perform the addressing, writing and reading of the data from the storage media by directing these beams at a specific region on the surface of the media. Writing is achieved by remembering the interference pattern formed by these beams at this region. Reading is achieved by detecting a reconstructed light beam as it exits the storage medium, the data then being extracted therefrom. Addressing is achieved by the positioning of the laser beams, and this is typically done through the mechanical movement of mirrors or lenses; however, the storage media itself can be moved relative to fixed laser beams.
The holographic storage media can be comprised of a photosensitive polymer material that has a plurality of constituents that react when exposed to an appropriate level of illumination. During a data recording operation, a data encoded light beam and a reference light beam are interfered in a specific location on the surface of the holographic storage media to create an interference pattern, which interference pattern represents the Fourier transform of the data encoded on the data encoded light beam. The interference pattern causes differing levels of polymerization within the holographic storage media to "fix" the interference pattern within the storage media. When the constituents required for the polymerization are completely utilized, no further polymerization will result. However, until the constituents are completely utilized or "depleted" the holographic storage media will be light sensitive.
The present holographic data storage systems utilize a single fixed media that is aligned with respect to the Read/Write optics. This will typically require an overall "light tight" packaging system wherein the optics and the holographic storage media are disposed in a single housing light tight enclosure. Once disposed in the housing, data can be recorded onto the storage media until it is completely "saturated". However, care must be taken when removing the storage media or replacing it with another "virgin" storage media to prevent depletion of unused constituents.